我們仔細看昨天的流程會發現，要調用Google Drive之前一定要先拿使用者的token去建立*http.Client然後再交給drive.NewService去作操作，調用其他Google的API也是相似的作法，也就是要先有GoogleOAuth才有GoogleDrive，所以我們先來微調一下昨天的程式。

// oauth.go
package google

import (
	"context"
	"log"

	"golang.org/x/oauth2"
	"golang.org/x/oauth2/google"
	"google.golang.org/api/drive/v3"
	"google.golang.org/api/option"
)

type GoogleOAuth struct {
	Config *oauth2.Config
}

func NewGoogleOAuth(clientID string, clientSecret string, redirectURL string) *GoogleOAuth {
	return &GoogleOAuth{
		Config: &oauth2.Config{
			ClientID:     clientID,
			ClientSecret: clientSecret,
			Endpoint:     google.Endpoint,
			Scopes:       []string{drive.DriveScope},
			RedirectURL:  redirectURL,
		},
	}
}

func (oa *GoogleOAuth) OAuthLoginURL() (oauthURL string) {
	oauthURL = oa.Config.AuthCodeURL("state-token", oauth2.AccessTypeOffline)
	return oauthURL
}

func (oa *GoogleOAuth) UserOAuthToken(authCode string) (*oauth2.Token, error) {
	token, err := oa.Config.Exchange(context.TODO(), authCode)
	if err != nil {
		log.Printf("Unable to retrieve token from web %v", err)
		return nil, err
	}
	return token, nil
}

func (oa *GoogleOAuth) NewGoogleDrive(ctx context.Context, tok *oauth2.Token) (*GoogleDrive, error) {
	client := oa.Config.Client(ctx, tok)
	srv, err := drive.NewService(ctx, option.WithHTTPClient(client))
	if err != nil {
		log.Printf("Unable to retrieve Drive client: %v", err)
		return nil, err
	}
	return &GoogleDrive{
		Service: srv,
	}, nil
}

我們把NewGoogleDrive拉到oauth.go，並且變成GoogleOAuth的方法，然後把原本NewClientByUserToken放進去NewGoogleDrive裡面，畢竟NewClient現在的目的就是去NewGoogleDrive，我們讓GoogleOAuth變成對外的統一入口，來操作各種GoogleAPI。如果以後有其他GoogleAPI服務要用，就在這邊繼續NewGoogleXXX就好了。而drive.go就保持存放專門操作google drive的部分~

接著我們在/adapter/google下建立interface.go，讓GoogleOAuth的方法對外

package google

import (
	"context"

	"golang.org/x/oauth2"
)

type GoogleOAuthI interface {
	OAuthLoginURL() (oauthURL string)
	UserOAuthToken(authCode string) (*oauth2.Token, error)
	NewGoogleDrive(ctx context.Context, tok *oauth2.Token) (*GoogleDrive, error)
}

下一步，我們來去實現Service層

1. 首先，像Sample Service一樣，我們建立以下對應的檔案

   

2. 建立interface.go並宣告DriveServiceGoogleOAuthI ，我們複製GoogleOAuthI的方法，讓GoogleOAuth能被注入近來這個Service。

   // interface.go
   package drive
   
   import (
   	"context"
   
   	"github.com/onepiece010938/Line2GoogleDriveBot/internal/adapter/google"
   	"golang.org/x/oauth2"
   )
   
   type DriveServiceGoogleOAuthI interface {
   	OAuthLoginURL() (oauthURL string)
   	UserOAuthToken(authCode string) (*oauth2.Token, error)
   	NewGoogleDrive(ctx context.Context, tok *oauth2.Token) (*google.GoogleDrive, error)
   }
   

3. 建立service.go，讓New一個GoogleDriveService的時候，要放入有實現DriveServiceGoogleOAuthI的實例。

   // service.go
   package drive
   
   import "context"
   
   type GoogleDriveService struct {
   	driveServiceGoogleOA DriveServiceGoogleOAuthI
   }
   
   type GoogleDriveServiceParam struct {
   	DriveServiceGoogleOA DriveServiceGoogleOAuthI
   }
   
   func NewGoogleDriveService(_ context.Context, param GoogleDriveServiceParam) *GoogleDriveService {
   	return &GoogleDriveService{
   		driveServiceGoogleOA: param.DriveServiceGoogleOA,
   	}
   }
   

4. 建立drive_service.go，先寫一個ListFiles()，這部分之後還會改，這邊先確定可以正確調用GoogleOAuth和GoogleDrive的方法。

   // drive_service.go
   package drive
   
   import (
   	"context"
   	"log"
   )
   
   func (dr *GoogleDriveService) ListFiles(authCode string, ctx context.Context) (map[string]string, error) {
   	tok, err := dr.driveServiceGoogleOA.UserOAuthToken(authCode)
   	if err != nil {
   		log.Panicln(err)
   		return nil, err
   	}
   	d, err := dr.driveServiceGoogleOA.NewGoogleDrive(ctx, tok)
   	if err != nil {
   		log.Panicln(err)
   		return nil, err
   	}
   
   	result, err := d.ListFiles(10)
   	if err != nil {
   		log.Panicln(err)
   		return nil, err
   	}
   
   	return result, nil
   }
   

5. 接著我們到application.go，把Drive Service註冊進Application中，並且提供外部NewApplication的時候，放入實現google.GoogleOAuthI的oauth ，然後注入到GoogleDriveService中。

   // application.go
   package app
   
   import (
   	"context"
   
   	"github.com/line/line-bot-sdk-go/v7/linebot"
   
   	"github.com/onepiece010938/Line2GoogleDriveBot/internal/adapter/dynamodb"
   	"github.com/onepiece010938/Line2GoogleDriveBot/internal/adapter/google"
   	serviceDrive "github.com/onepiece010938/Line2GoogleDriveBot/internal/app/service/drive"
   	serviceSample "github.com/onepiece010938/Line2GoogleDriveBot/internal/app/service/sample"
   )
   
   type Application struct {
   	SampleService *serviceSample.SampleService
   	DriveService  *serviceDrive.GoogleDriveService
   	LineBotClient *linebot.Client
   }
   
   func NewApplication(ctx context.Context, dynamodb dynamodb.DynamodbI, oauth google.GoogleOAuthI, lineBotClient *linebot.Client) *Application {
   
   	app := &Application{
   		LineBotClient: lineBotClient,
   		SampleService: serviceSample.NewSampleService(ctx, serviceSample.SampleServiceParam{
   			SampleServiceDynamodb: dynamodb,
   		}),
   		DriveService: serviceDrive.NewGoogleDriveService(ctx, serviceDrive.GoogleDriveServiceParam{
   			DriveServiceGoogleOA: oauth,
   		}),
   	}
   	return app
   }
   

6. 最後我們到server.go，在StartNgrokServer()和NewGinLambda() 做NewApplication的地方補上NewGoogleOAuth並注入到Application中

   // StartNgrokServer()
   oauth := google.NewGoogleOAuth(os.Getenv("ClientID"), os.Getenv("ClientSecret"), os.Getenv("RedirectURL"))
   
   app := app.NewApplication(rootCtx, db, oauth, lineClient)
   

   // NewGinLambda()
   googleClientID, err := ssmsvc.FindParameter(rootCtx, ssmsvc.Client, "GOOGLE_CLIENT_ID")
   	if err != nil {
   		log.Println(err)
   	}
   	googleClientSecret, err := ssmsvc.FindParameter(rootCtx, ssmsvc.Client, "GOOGLE_CLIENT_SECRET")
   	if err != nil {
   		log.Println(err)
   	}
   	redirectURL, err := ssmsvc.FindParameter(rootCtx, ssmsvc.Client, "REDIRECT_URL")
   	if err != nil {
   		log.Println(err)
   	}
   	oauth := google.NewGoogleOAuth(googleClientID, googleClientSecret, redirectURL)
   
   	app := app.NewApplication(rootCtx, db, oauth, lineClientLambda)
   

那我們今天就先到這兒，明天見囉~